Thursday, 2 August 2018

Is it OK to PWM a current source?


I want to control power RGB LEDs, for efficiency and safety they are better to be driven by a current source. I can use either linear or buck converters. I made a linear current source using LM317.


enter image description here


I PWMed the input (Vin) and it worked fine. Is it OK if I PWM the output(using a MOSFET right before the load)? As I learned in theory if the output is left open the output voltage reaches infinity (hear maybe a maximum of input voltage), so as I turn the MOSFET on a high voltage goes to the LED momentarily and might damage it after a while.


I think a decent step-down LED driver is PT4115E (Datasheet) it has a PWM pin. Are chips like this OK for driving LEDs that duty cycle may change several times per second?





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